After graduating in 1978 at the Faculty of law of the University of Leiden, Jaap Hage worked at the same University as scientific assistant/Assistant Professor until 1989. In 1983 he studied also Philosophy and in 1987 he obtained a PhD for the thesis on legal philosophy and meta-ethics, entitled “Feiten en betekenis”.
From 1989 to 1991, he worked at the Department of computer science, on a research project on the user interface of software to protect from software maintenance. From 1991 he worked first as Associate Professor and from 2006 as a professor at the Law Faculty of the Maastricht University at the Department of interdisciplinary study. His research is in the field of the theory of law, with special emphasis on the logic of legal reasoning and the general concepts of law.